For many years, sealing rings such as 0-ring seals or the like, have been provided in rotary plug valves for sealing off the fluid when the valve is moved to the closed position. When the sealing ring is provided in a groove in the valve seat of the housing member rather than on the plug member, the groove is usually provided around the outlet or downstream port of the housing member. It was the feeling that by positioning such a sealing ring around the downstream port of the housing member, the pressure of the fluid passing through the valve tended to hold the sealing ring in its groove when the valve was being operated between the open and closed positions. However, this type of arrangement has not been too satisfactory for commercial use as it has proved costly to manufacture such a rotary plug valve since it was difficult to machine the groove for the sealing ring in the housing member. Also if the valve was inadvertently installed into a fluid line so that the sealing ring in the housing member was around the upstream or inlet port of the housing member, then the valve operated unsatisfactory because the flow through the valve when the valve was being opened and closed caused the sealing ring to be drawn out of its groove and to be clipped when the port openings of the plug member passed by the same.
Since it is far more desirable to provide a sealing ring in a groove on the plug member of the rotary plug valve because the manufacture of the rotary plug valve is simplified and is less costly, there has been a trend over the past years to provide such a groove for the sealing ring on the plug member between its port openings rather than in the valve seat of the valve housing member. In theory, it was originally believed that the sealing ring must surround the inlet port when the valve was in the closed position and the sealing ring was carried by the plug. The pressure of the fluid in the line during opening and closing of the valve was felt to be sufficient to hold the sealing ring in its groove on the plug. However, it has been found that this arrangement is not necessarily foolproof and there was still clipping of sealing rings as the valves approached full open position. Additionally, this type of rotary plug valve had the disadvantage in that it could not be a two-way valve and if by chance the valve was inserted into the fluid pressure line in the wrong way so that the sealing ring surrounded the downstream port of the valve housing member when the valve was closed, the differential pressure across the sealing ring as a portion or segment of the same passed the downstream port of the valve housing member during closing caused the sealing ring to be lifted from its groove and a clipping of the ring resulted.
In an effort to improve the rotary plug valves, various means have been used in the past to try to retain the sealing rings in their grooves both when the groove is provided around one of the ports in the valve housing member as well as on the surface of the plug member between the plug member's port openings. In this respect, rotary plug valves for high-pressure fluid distribution systems have been designed with special means for trying to equalize the pressure across the sealing ring, to maintain the sealing ring in its groove, or means have been provided which will guide the sealing ring back into its groove as the plug member is being rotated between the open and closed positions of the valve. The various arrangements heretofore provided all had the disadvantage in that while they did help maintain the O-ring seal in its groove for a particular flow situation, the rotary plug valve was not capable of two-way flow. In this respect, depending upon the location of the sealing ring, there was always a situation in which the sealing ring would not function correctly in all conditions of flow, whether forward flow through the valve or reverse flow through the valve, and consequently, undesirable clipping of the sealing ring could occur.
The problem of sealing ring clipping or shearing in rotary plug valves has been a constant source of trouble in the industry and a solution had to be found so that the rotary plug valves would be completely servicable for flow in both directions and could operate without the sealing ring ever being clipped. The solution to this problem which resulted in the present invention will appear later in the specification under the heading "BRIEF SUMMARY OF THE INVENTION" as well as under the heading "DETAILED SUMMARY OF THE INVENTION."
Prior arrangements relating to but not suggesting the present invention are disclosed in the following United States Patents:
______________________________________ Number Name Date ______________________________________ 2,433,732 C. A. Brown Dec. 30, 1947 2,510,514 F. H. Mueller June 6, 1950 2,547,116 W. E. Gould April 3, 1951 2,547,831 F. H. Mueller April 3, 1951 2,604,293 D. L. Phillips July 22, 1952 3,480,042 F. H. Mueller et al. Nov. 25, 1969 ______________________________________
While the above listed patents disclose various arrangements of rotary plug valves which are provided with means for attempting to prevent the sealing ring of the plug valve from being clipped during opening or closing of the plug valve, none of these patents suggest an arrangement which completely eliminates the problem of clipping of a sealing ring in a rotary plug valve regardless of the installation of the plug valve in a fluid pressure distribution system nor do the patents disclose an arrangement which provides utility to a rotary plug valve for flow through the valve in either direction.